A transparent and conductive oxidized film, such as an Indium Tin Oxide (ITO) film, is formed on a workpiece like an insulative substrate which is formed of glass or a plastic resin, and which is utilized for touch panels, etc. A film formation apparatus, that has a target formed of a film formation material placed in a chamber that is a sealed container, is applied for film formation. A sputter gas containing oxygen is introduced into the chamber, a DC voltage is applied to the target to obtain the plasma of the sputter gas and to produce ions, and the ions collide with the target. Material particles beaten out from the target are deposited on the workpiece, and thus a film is formed thereon.
At the time of film formation process, the film formation material sticks not only to the surface of the workpiece but also to the internal wall of the chamber. When the film formation process is repeatedly executed, the amount of sticking material increases. The film formation material sticking to the internal wall of the chamber produces an outgas. This outgas contains oxygen, and this oxygen is also ionized by plasma. Hence, upon repeating the film formation process, the amount of oxygen increases. When, in the film formation process, the appropriate amount of oxygen is not maintained, the resistance value may increase in the ITO film formed. That is, the quality of the products becomes non-uniform, and result in a possibility of a defective product.
It is known that, when the oxygen in the chamber increases, the film formation speed decreases. For example, JP S58-94703 A proposes a technology of providing, in the chamber, a measuring element that measures the film formation speed, and of adjusting the amount of oxygen introduced to the chamber in accordance with the decrease of the film formation speed. However, the decrease of the film formation speed indicates a state which the film formation is performed with the total amount of oxygen present in the chamber already exceeding the appropriate amount. Hence, even if the amount of oxygen to be introduced to the chamber is adjusted at this state, the quality may become non-uniform, and result in a possibility of a defective product.
The present disclosure has been made to address the foregoing technical problems, and an objective is to provide highly reliable film formation apparatus and film formation method capable of producing products which have an excellent quality and little variability in quality even when a film formation process is repeatedly executed.